1. Field of the Invention
The present invention relates to production of hybrid optoelectronic devices which integrate active optoelectronic and passive optical components into novel hybrid optical devices to be used in optoelectronic systems.
2. Discussion of the Background
In customer optoelectronic systems, large bandwidth, polarization insensitive, low loss devices are required for multi-channel broadcasting. Optical component processing based on self-imaging devices such as multimode interference (MMI) devices is an attractive choice for fabrication. Indeed, due to excellent optical properties and ease of fabrication, multimode interference (MMI) devices have already found applications in laser modulators, splitters, switches, and receivers. Production MMI power splinters, as compared with conventional 1xc3x972 waveguide branches, yield devices with smaller dimensions and do not suffer from non-uniformity of output power as a result of sharp edges near the waveguide branches.
From a component viewpoint, a subscriber loop requires massive power splitting for distribution purposes. As needs in the customer loop intensify, ultra small-dimension, large bandwidth, low loss, low reflection and polarization insensitive devices will be required to accomplish a variety of optical processing, such as for example signal splitting. Furthermore, wavelength division multiplexing (WDM) soon will impact nearly all optical network systems. WDM, by itself, requires integration of a number of active and passive optical components including multi-wavelength sources, multiplexers, wavelength add-drop filters and switches. Due to the diverse characteristics of each of these components, integration onto a singular substrate is an imposing problem with conventional fabrication procedures and standard optical glass materials.
Furthermore, the increasing demand for optoelectroninc systems presents a need in long distance free space applications for optoelectronic systems utilizing steerable high power surface emitting lasers. The development of high power diode lasers with integrated steering capability will play a significant role in free space tracking and communication. Here, as with WDM, integration of optical components onto a singular substrate represents a complex problem.
Sol-gel processing, which utilizes low temperature polymerization, has stimulated considerable research. The sol-gel process can be considered as a method for producing glass and ceramic materials from metallorganic precursors by low temperature polymerization reactions. H. K. Schmidt in xe2x80x9cSol-gel and polymer photonic devices,xe2x80x9d SPIE Critical Review, vol. CR68, pp. 192-203, 1995 discloses sol gel processing as a tool for making diverse transparent materials with interesting optical or photonic properties.
However, one obstacle for application of sol-gel inorganic materials into optical devices is the limitation imposed by the maximum attainable crack-free sol-gel glass thickness. Glass-on-silicon technology compatible with single mode fiber for 1.55-xcexcm window requires channel waveguides typically greater than 1xcexcm in thickness. Fabrication of such components based on oxygen-metal-oxygen materials normally demands iterative cycles of deposition, baking at temperatures around 1000xc2x0 C., and dry etching. Thus, these processes are costly and time consuming.
Introduction of non-volatile organic groupings with a metal backbone has led to interesting materials, such as organically modified silicon and zirconium alkoxides as discussed by H. K. Schmidt, supra, that have substantially reduced the processing demands.
Relaxation in the processing temperature by incorporating organic groupings, used either as a host or a guest, which can modify the inorganic backbone and reduce the connectivity of the sol-gel network allows thicker film deposition and a lowering of the processing temperature compared to sols which do not include the organic groupings. Furthermore, M. A. Farad et al., in Applied Optics vol. 37, pp. 2429-2434, 1998, and in Electronics Letters, vol. 34, pp. 1940-1941, 1998 disclose use of photopolymerizable organic groups, utilizing organic groupings containing unsaturated bonds, Cxe2x95x90C double bond in vinyl or methacryl groups, to enables photopolymerization, and thus, the capability to pattern sol-gel glasses using lithographic techniques. In U.S. Pat. No. 6,054,253, M. A. Fardad et al. disclose photo-patternable organically modified silicates doped with modified zirconium and buthoxyaluminoxytriethoxysilane. However, these materials were require rigorous synthesis and patterning procedures, not conducive to optical device integration.
Thus, a number of issues regarding loss inherent from the sol-gel processing have not been resolved which limit the application of sol-gel processing and thus restrict optical device integration, especially between diverse active and passive optical components. These issues include inherent losses in the sol gel glasses at the operating frequency, unintentional losses due to light scatter at sol-gel glass/air interfaces, and improper design of passive optical components.
As a consequence of the complexities of the integration process and the lack of a suitable sol-gel medium, optoelectronic systems coupling light output from photoelectronic devices into power splitters and beam steering elements have not been integrated onto a singular substrate.
Accordingly, one object of the present invention is to provide a sol-gel application process which overcomes shortcomings of traditional sol gel materials and has the requisite low-loss, polarization insensitivity, and large bandwidth needed for integration of active and passive optical components into complex optoelectronic devices.
Another object of the present invention is to integrate low-loss and low-cost sol-gel based glass waveguides with active optoelectronic devices to provide a platform for hybrid optoelectronic integration, wherein silicon substrates can be used as heat sinks and optical benches for optoelectronic chips such as laser diodes, coupling output from the optoelectronic devices into passive glass waveguides (filters, splitters, etc.)
Still a further object of the present invention is to provide a sol-gel with low internal loss and excellent surface smoothness to minimize both internal absorption of light and light scattering, both of which diminish optical transmission through a device.
In a preferred embodiment of the present invention, the sol-gel material is derived from a sol containing methacryloxy propyl trimethyoxysilane (MAPTMS) and aluminum alkoxide and hydroxy methyl methaacryloxy propiophene (HMPP) diluted to appropriate viscosity with ethanol. The sol-gel material is aged for a prescribed period of time, spun onto a substrate, and cured for a prescribed period of time to produce the afore-said surface smoothness properties.
Another object of the present invention is to provide a sol-gel application and curing process which produces patterned sol-gel optical structures having improved surface properties and predetermined dimensions, wherein unwarranted light scattering within the hybrid optoelectronic devices is prevented.
Accordingly, a further object of the present invention is to provide a fabrication process to produce the complex optoelectronic devices in which design tolerances are specified to minimize optical losses, especially at interfaces between different optical components.
In one embodiment of the present invention, vinyltriethoxysilane (VTES) forms at least one of a cladding layer and a planarization layer above the above-mentioned sol-gel optical components.
Specifically, a further object of the present invention is to provide a sol-gel-based MMI power splitter integrated with distributed Bragg reflector (DBR) laser.
In addition, another object of the present invention is to provide, without sol-gel processing, an integrated optoelectronic device such as for example a distributed Bragg reflector laser which includes an outcoupling layer which upon current injection changes the index of refraction of the outcoupling layer and thus electronically controls a direction of an output light.
These and other objects are provided for in the present invention by a hybrid optoelectronic device and method of producing the hybrid device in which the hybrid device includes a substrate with an input region configured to accept input light, a sol-gel glass multimode interference region coupled to and contiguous with the input region and configured to accept and replicate the input light as multiple self-images, and a sol-gel glass output region contiguous with the multimode region and configured to accept and to output the multiple self-images. Alternatively, the hybrid optoelectronic device can include a substrate with a photoelectronic device, a surface resonator including a light-emitting part of the photelectronic device and configured to resonate light from the photoelectronic device to produce a laser light, and a grating outcoupler contiguous with the surface resonator and configured to diffract the laser light outward from the grating outcoupler and to electrically vary an index of refraction of the grating outcoupler and direct emission of the laser light from the outcoupler